Communication from a user to a computer may be accomplished in several ways using a variety of input devices. A traditional direct input device is a typewriter keyboard which can be used to transmit alphanumeric data directly into the computer. Most microcomputer systems also have a cathode ray tube (CRT) monitor which displays to the operator the text being supplied to the computer and also allows output communication from the computer to the user. The CRT display may also be used to generate graphics, and the operator can use the CRT screen to relate interactively with the computer by manipulating data or graphic images on the screen. One way in which the user and computer may actively interact is by allowing the user to move a cursor or pointer spot about the CRT screen in a manner of movement or to a position which has significance to the computer. Various devices have been developed which allow the user to selectively move the cursor spot on the CRT screen, including keyboard keys which direct movement of the cursor sideways or up or down, light pens, joy sticks, rolling balls and so-called "mouses." The motions of the user's hand are translated by these devices into commands to the computer to cause it to move the cursor in a direction indicated by the user.
While many devices presently exist which allow interactive cursor positioning, they are, by and large, not well integrated with the range of motions and actions normally employed by a typist when inputing alphanumeric information into a computer through a normal keyboard. Specifically, almost all commonly used cursor positioning devices require that the user remove his or her hand from the keyboard to reach the cursor positioning device, and generally the user's eyes must be diverted from the screen to the manipulatable device, at least momentarily, while the device is being held and used. Where cursor position manipulations on the CRT screen are intended to be integrated with inputing of alphanumeric information through the keyboard--as in word processing where the cursor positioning may be used to designate to the computer points of corrections, deletions, or insertions--a substantial loss in convenience and efficiency results due to the diversion of the user's attention from the keyboard. For example, when using a mouse-type positioner, the user must move his hand from the keyboard to grasp the mouse and must then push the mouse over a flat surface next to the keyboard until the cursor reaches the desired spot on the CRT screen. The user then removes his hand from the cursor and must find the proper position for his hand on the keyboard to begin typing operations again. Such off-keyboard cursor control devices also require the availability of additional clear space next to the keyboard and suffer from the greater wear and tear associated with the use of a mechanical element as compared with electronic components. Non-mechanical touch pad positioners have been developed which allow a user to control the cursor by moving the position of contact of his finger about the touch pad. While such touch controlled devices require less space and are less prone to mechanical problems, the prior touch pads typically allow the user to control the displacement of the cursor in only a relatively few discrete angular directions and are susceptible to a variety of noise sources.